Variable-pitch propellers are particularly known, wherein the pitch is given automatically by activating the propeller itself, comprising a cylindrical propeller casing, on which the propeller blades are pivoted according to a cross direction relatively to the propeller casing axis itself, a shaft, that is coupled coaxially to the propeller casing, means for transmitting the rotary movement from the shaft to the propeller casing, as well as a kinematic system for regulating the rotary motion of each blade around its own pivot axis to the propeller casing, preferably adapted to transform the rotary motion of the shaft in a rotary motion of each blade around its own pivot axis.
To allow the afore mentioned kinematic system activation to transform the shaft rotation in the blade rotation, the transmission motion means provide that the shaft might turn in ad idle manner relatively to the propeller casing, at least for an angular predefined range. The idle rotation of the shaft in such an angular range, the propeller casing being substantially stationary most of all because of friction, causes, thanks to the afore mentioned kinematic system of regulation/transformation, the relative rotation of the blades relatively to the propeller casing, inducing the consequent variation of their pitch.
Such a propeller type of the known art might as well provide that the blades, when the torque on the shaft will fail, and because of the fluid dynamic stresses to which the propeller itself is subjected, could be free of disposing in a “rest” configuration, predefined during the designing step.
For example, in the case of motorboat engines, such a rest configuration corresponds to a predefined propeller pitch, whereas, in the case of sailing boats provided with auxiliary engines, when the torque will fail, the propeller is free to dispose in the “feathered” position, that is to offer the smallest fluid dynamic resistance is possible (propeller disposed according to an infinite pitch).
To such a “rest” arrangement of the blade corresponds as well, the consequent shaft arrangement at the beginning of the angular range of free rotation between the shaft and the propeller casing, thanks to the integral kinematic system of transformation, so that when the shaft will be subjected to a torque again, it will turn idly relatively to such a propeller casing in the afore mentioned angular range, causing the corresponding blade rotation according to the desired pitch.
The Italian patent IT 1 052 002, in the name of Massimiliano Bianchi, teaches to realize such a variable-pitch propeller in the feathered position, particularly for sailing boats, wherein the shaft and the propeller casing are mutually coupled by two coplanar teeth and that are orthogonal to the propeller axis itself. When the propeller blades are in the feathered position, being the propeller stationary, such a teeth are spaced out so that the rotationally subsequent shaft activation, whether in a sense or in the countersense, will cause its idle rotation for some angular range, to which the blade rotation corresponds relatively to the cylindrical casing and then the pitch changing thereof, thanks to an appropriate kinematic system of the pinion and gear wheel type.
Although such a propeller is very simple, and thereby strong, referring to a structural aspect, and provides that the propeller blades might dispose automatically according to a first pitch, that is according to a certain incidence angle relatively to the shaft, being adapted to the boat advance and according to a different pitch, adapted to the boat moving backwards, by such a propeller it is not possible to obtain a discrete or continuous variation of the pitch upon varying the operating conditions of the propeller itself.
That is, during the designing step once the most convenient blade pitch for the ahead movement is determined, and the most convenient pitch for the astern movement of the boat is determined, that is given, in addition to the blade shapes, also by their the rotation angle relatively to the propeller cylindrical casing, it is not more possible for the operator to change such a rotation angle for modifying the pitch during the propeller operation.
To compensate for such a drawback, variable-pitch propeller have been proposed, wherein the blade rotation relatively to the propeller casing, around their pivot axis on the latter, is driven by a mechanism that, not being integral with the shaft, but at most cooperating with it, might be manually operated also during the propeller operation itself.
For example, the European Application EP 0 328 966 A1 in the name of BIANCHI, teaches to realize such a mechanism, wherein a fluidic operated ram induces the shift of a toothed sleeve that, conveniently shaped, allows the pinion rotation, engaged in turn with the gear wheels that are integral to the blades. Ram manually operating causes the pinion and gear wheels rotation, thereby defining the incidence angle variation of the same blades, relatively to the shaft.
Such a solution, even if allowing the operator to dispose the propeller blades according to the most efficient pitch, according to the propeller operating conditions, provides that the operator will manually determine such a propeller pitch and thereby will impose to the operator a never ending attention to such an operating conditions, on the other hand without the guarantee of obtaining an optimal propeller efficiency, because of the discretion of such a manual operation.
It is an object of the present invention to realize a variable-pitch propeller, for example of the feathered type, that would not present the afore mentioned drawbacks of the known art, and therefore that would allow an efficient variation of its pitch, that is of the blade incidence angle relatively to the shaft, that could be obtained continuously and that could be completely automatic. Another object of the present invention is to realize a variable-pitch propeller, having an extremely simply structure, wherein the propeller pitch will adapt automatically and efficiently to the different dynamic conditions to which the propeller is subjected while it is operating.